How about keeping the lid down?

It can be. Agents used to clean the bowl can cause problems.

Try placing your cats water bowl on the floor next to the toilet or just
outside the bathroom door. Works for me. :c)

Judy and Matilda, who's water bowl sits just outside the bathroom door.

How about letting a little fresh water drip from the faucet into a bowl in
the sink?  I did this when I went away even thought I had a pet sitter and
when I came back I found my baby kitten wants to play with dripping water
and drink from the faucet.  She cries for me to turn on that water!

--
  Barb
  I can only please one person a day.
  Today is not your day.
  Tomorrow doesn't look good either.

Like Judy said, if you use chemicals it can be.

To wit, we had caught Neresse drinking from the toilet, in favor of a
small bowl of water left for her, when we were keeping her isolated in the
bathroom a while back.  It didn't really harm her - if anything, it
encouraged us to keep the commode scrupulously clean so she could drink of
it without getting worse, and we just rather she drank from there than not
at all (she was already having problems with dehydration).

Also remember that dogs will do this as well with little to no ill effect.
It looks kinda funky, but they'll do it.  It's this convenient and
renewale source of water to them, I guess.